Ambient light, also known as diffuse environmental light, is light that is present all around the Scene and doesn’t come from any specific source object. It can be an important contributor to the overall look and brightness of a sceneA Scene contains the environments and menus of your game. Think of each unique Scene file as a unique level. In each Scene, you place your environments, obstacles, and decorations, essentially designing and building your game in pieces. More info
See in Glossary.
Ambient light can be useful in a number of cases, depending upon your chosen art style. An example would be bright, cartoon-style renderingThe process of drawing graphics to the screen (or to a render texture). By default, the main camera in Unity renders its view to the screen. More info
See in Glossary where dark shadows may be undesirable or where lighting is perhaps hand-painted into textures. Ambient lightLight that doesn’t come from any specific direction, and contributes equal light in all directions to the Scene. More info
See in Glossary can also be useful if you need to increase the overall brightness of a scene without adjusting individual lights.
Ambient light settings can be found in the Lighting window.